May, June, and September are the best months — warm but not punishing, with long evenings and not too many day-trippers. July and August can be hot (often 32–35°C) and the centre fills with tour buses from late morning to mid-afternoon; arrive before 10am or stay overnight to see the town empty out.
Late September is the highlight of the year for many: the Volterra AD 1398 historical festival takes over the town on the last weekend of August with costumed parades, jousts, and medieval markets. Truffle season runs October to December — Volterra is in the heart of one of Italy's main white-truffle territories, and several restaurants run set truffle menus.
Winter is quiet and atmospheric. The town's stone buildings hold the cold and the wind whips off the surrounding ridges; bring layers.